Electronic equipment often employs printed circuit boards or cards. These cards typically are mounted in a chassis or card rack by stacking the cards in row alignment with one another. Row alignment in the chassis is defined by slotted or spaced surfaces within or on the chassis, with each card placed in a slot or between a pair of spaced surfaces.
Many applications for such retainers require that the retainer secure a printed circuit card to the chassis under severe shock and vibration conditions. This is particularly true for retainers used to secure circuit cards in equipment for spacecraft, or military aircraft.
In addition, the printed circuit board chassis often does not allow sufficient cooling air or fluid to pass over the circuit board, particularly where the chassis must be sealed from the surrounding environment, or where the chassis is densely packed with circuit components. To provide adequate cooling for components on the circuit card, heat generated on the circuit card is conducted to an edge of the circuit card, through a metal heat sink, inner copper planes, or a heat pipe attached to the circuit card, and then transferred by thermal conduction through the chassis to a heat exchanger or plenum operatively attached to the chassis. In order to achieve the required heat transfer, the edge of the circuit card must be clamped securely by the retainer against a clamping surface, of the chassis or heat sink, with enough force, directed normal to the card, to ensure intimate contact of the edge of the card with the clamping surface of the chassis or heatsink.
In one prior approach to retaining circuit cards, the edge of the card is positioned within a channel between a pair of oppositely facing surfaces. A screw-actuated wedge locking device installed in the channel between one of the surfaces and the card is utilized for forcing the edge of the card into contact with the other surface, to secure the card against movement and to clamp the edge of the card against the clamping surface to facilitate heat transfer from the edge of the card into the clamping surface. Such wedge locking type retainers are sometimes attached to the edge of the circuit card. U.S. Pat. No. 4,823,951 to Colomina, U.S. Pat. No. 5,290,122 to Hulme, and U.S. Pat. No. 6,285,564B1 to O'brien, describe such wedge locking circuit card retainers. Such wedge locking type retainers are also sold under the trade name “series 226 Card-lock” by Calmark Corporation, of San Gabriel Calif., United States of America.
Screw actuated wedge locking retainers have several disadvantages. The mechanism is somewhat complex, given the simple function to be performed, thereby driving up the cost of the retainers and installation into the chassis. The complexity and necessity for angular movement of the wedges makes this type or retainer larger than is desirable in densely packed electronic chasses. The screw must also typically be made of steel or a high strength alloy, which adds undesirable weight. A pair of oppositely facing surfaces on the chassis is also required, thereby adding undesirable complexity to the chassis.
In another prior approach to securing circuit cards in a chassis, retainers having a plurality of leaf spring members have been utilized. One such leaf-spring type retainer is provided under the trade name “Series nw125 and nw126 Card Retainer” by Calmark Corporation of San Gabriel Calif., United States of America. U.S. Pat. Nos. 3,231,785 and 3,950,057 to Calabro disclose other forms of leaf finger spring retainers.
In some forms of prior leaf spring retainers, such as the Series nw125 and nw126 Card Retainers, by Calmark Corporation, one of the opposing surfaces can be eliminated from the chassis by securing the card retainer to the chassis adjacent to the clamping surface. Right and left handed retainers must be provided, however, depending upon the orientation of the clamping surface with respect to the retainer. Such leaf spring retainers must also typically be made of a high strength material such as stainless steel, or beryllium copper, thereby making them heavier than is desirable. Such leaf spring type retainers are also relatively bulky, consuming more package volume than is desirable. The additional steps of riveting or otherwise attaching the retainer to the chassis also add undesirable expenditures of time and cost during fabrication.
It is desirable, therefore, to provide an improved retainer, apparatus, and method for retaining a circuit card against a clamping surface of a chassis or heatsink.